1. Field of the Invention
The present invention relates to an optical information medium comprising one disc formed of a transparent substrate and having an information recording area at least at a main surface thereof and another disc which is bonded to the one disc.
2. Prior Art
A digital video disc (DVD) capable of recording and reading information of a high-density put into practical use associated with the recent development and practical utilization of a laser having a short wavelength. The optical information medium of this type can adopt a structure in which two discs are bonded.
A read-only optical information medium having such a structure for bonding two surfaces of discs has a hole at the center thereof and an inner peripheral side information non-recording area at the outside thereof. A pair of discs which are bonded to each other comprise a transparent substrate and an information recording area provided outside the inner peripheral side information non-recording area on the main surface of one of the discs, and a pit serving as an information recording means formed on the information recording area, and a reflecting layer formed of a metal film and provided on the pit. Further, as an optical information medium capable of recording information, a tracking guide is formed on the information recording area provided on at least one disc, and an optical recording layer formed of organic dyes, etc. is formed on the tracking guide by a means such as a spin-coating process. Still further, a reactive curing resin as an adhesive is coated on the surfaces of a pair of discs by means of the spin-coating process or a screen printing, and the coated surfaces are laid on top of another to oppose each other, and two discs are bonded to each other by the adhesive set forth above.
In the optical information medium, two discs are bonded by the adhesive as mentioned above. However, since the surface of the disc on which the inner peripheral side information non-recording area is provided is smooth, slippage is liable to occur between a clamper and the disc when the smooth surface is clamped by an optical information medium player so as to rotate the disc. As a result, there occurs a problem of faulty operation and non-reproduction of the record involved in the displacement of clamping position or rotating variation.
In the optical information medium set forth above, since the surface of the disc in the inner peripheral side information non-recording area is smooth, when the outer peripheral portion is grasped by hand, the disc is slippery and liable to be dropped. Accordingly, two surfaces of the optical information medium at the peripheral side portion are frequently normally grasped by fingers, thereby soiling the recording surface of the optical information medium with fats on the fingers.